There is a communication service of transmitting in store-and-forward system a message composed of characters from a transmitting side terminal device via one or more other networks or communication relay equipment of providers to a receiving side terminal device. Such a communication service has already been implemented in lots of countries as an embodiment in a known communication service called short message service, for example.
Meanwhile, an identical subscriber uses multiple terminal devices located in networks respectively operated by multiple network operators, or multiple subscriber numbers are used by a single terminal device. Such techniques have already been spreading.
Under the above situation, there have several proposals of using multiple subscriber numbers with a single terminal device. For instance, there has been proposed a communication method that enables the use of subscriber numbers with completely different service contents on a commonly used terminal device, and thereby selectively receiving a call or message with any one of the subscriber numbers (For example, see Patent Document 1).
In the proposal disclosed in the above Patent Document 1, a main subscriber number and a subsidiary subscriber number are registered in a rewritable database beforehand and the registered contents are changed as necessary, so that multiple subscriber numbers with service contracts different from each other are capable of being selectively used.